1. Field of the Invention
The present invention relates generally to a developer used for developing an electrostatic latent image formed on a photoreceptor and a developing method using the developer in an image forming apparatus such as a copying machine or a printer, and more particularly, to a developer used for carrying out reversal development of an electrostatic latent image formed on a positively charged amorphous silicon type photoreceptor and a developing method using the developer.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a copying machine or a printer has been so adapted as to form an electrostatic latent image on the surface of a photoreceptor, supply a developer to the photoreceptor from a developing device, develop the electrostatic latent image formed on the photoreceptor to form a toner image on the photoreceptor, transfer the toner image on a recording medium such as paper, then press a cleaning blade or the like against the surface of the photoreceptor, and remove toner particles or the like remaining on the surface of the photoreceptor.
As the above-mentioned photoreceptor various materials have been conventionally used for composing its photosensitive layer. Examples are an organic photoreceptor using an organic material, a selenium type photoreceptor using a selenium type material, and an amorphous silicon type photoreceptor using an amorphous silicon type material.
When an image is formed in the above-mentioned manner using such a photoreceptor, a filler such as talc or calcium carbonate produced from a recording medium such as paper, or a toner component may, in some cases, be film-formed upon adhering to the surface of the photoreceptor.
When the above-mentioned photoreceptor is an organic photoreceptor using an organic material as a material composing its photosensitive layer or a selenium type photoreceptor using a selenium type material as a material composing its photosensitive layer, the photosensitive layer is relatively soft. When the cleaning blade or the like is pressed against the surface of the photoreceptor after the transfer as described above to remove the toner particles or the like remaining on the surface of the photoreceptor, the surface of the photoreceptor on which the filler, the toner component or the like adheres is shaved by the cleaning blade or the like. Therefore, few problems particularly arise.
In the case of the amorphous silicon type photoreceptor using the amorphous silicon type material as the photosensitive layer, however, the photosensitive layer on its surface is harder than those of the organic photoreceptor and the selenium type photoreceptor. When the toner particles or the like remaining on the surface of the photoreceptor are removed by the cleaning blade or the like as described above, therefore, the surface of the photoreceptor is not shaved by the cleaning blade or the like, and the filler, the toner component or the like adhering to the surface of the photoreceptor remains, to be film-formed. Therefore, the image quality of a formed image is gradually degraded.
Also in the prior art, therefore, a method of carrying out development using a developer having magnetic resin carrier particles having magnetic fine particles dispersed in binder resin, magnetic powder carrier particles, and abrasive magnetic toner particles having abrasive material fine particles fixed to their surfaces, to grind the surface of an amorphous silicon type photoreceptor, as disclosed in Japanese Patent Laid-Open No. 323674/1993, and a method of externally attaching predetermined silicon carbide to the surfaces of toner particles or adding the silicon carbide to a developer, and carrying out development using the developer to grind the surface of an amorphous silicon type photoreceptor, to prevent the above-mentioned film-formation, as disclosed in Japanese Patent Publication No. 29982/1994 and Japanese Patent Publication No. 29983/1994.
Also in the methods disclosed in the gazettes, however, it is still impossible to sufficiently prevent a filler, a toner component or the like adhering to the surface of the amorphous silicon type photoreceptor from being film-formed. When the above-mentioned developer is used, the toner particles are not sufficiently charged, whereby the toner particles are scattered, a formed image is fogged, and the fluidity of the developer is decreased so that the developer is offset in a developing device, and the density of the formed image is made non-uniform